docs: def save_img(self, file_name=None, file_type="gif", mode='dot'):
          '''
          Saves the dot file as an image file
          '''
  
          if not file_name:
              warnings.warn(DeprecationWarning, "always pass a file_name")
              file_name = "out"
  
          if  mode == 'neato':
              self.save_dot(self.temp_neo)
              neato_cmd = "%s -o %s %s" % (self.neato, self.temp_dot, self.temp_neo)
              os.system(neato_cmd)
              plot_cmd = self.dot
          else:
              self.save_dot(self.temp_dot)
              plot_cmd = self.dot
  
          file_name  = "%s.%s" % (file_name, file_type)
          create_cmd = "%s -T%s %s -o %s" % (plot_cmd, file_type, self.temp_dot, file_name)
          os.system(create_cmd)